This invention relates to a method for treating podotrochlosis, or navicular disease, in the foot of a horse.
Podotrochlosis, also known as navicular disease or navicular syndrome, is a type of lameness affecting the forelimbs of horses. The condition is almost always bilateral and is most commonly seen in middle-aged performance horses, such as hunters or show horses, for example, that are confined or stall-kept, that have high physical demands placed on them, or that are required to continuously walk over hard surfaces, such as pavement or gravel. Fast-growing breeds with small feet, such as Quarter Horses or Thoroughbreds, are at a higher risk for developing the condition than are slower-growing breeds, such as draft horses, which have larger feet in comparison to their body size.
The actual cause of the condition is not clearly understood, and thus, is frequently referred to as a syndrome (a recurring group of symptoms of unknown cause), rather than a disease. Factors that contribute to the initiation of the condition include, but are not limited to, preferential breeding for body mass and small feet, poor conformation and poor or inappropriate shoeing, that can lead to a broken hoof-pastern axis, long toes and underslung heals. Each of these factors can place unusual pressure and stress on the navicular bone, causing inflammation and pain, which ultimately leads to lameness. Probst, S., xe2x80x9cNavicular Syndrome in Horses,xe2x80x9d University of Illinois, College of Veterinary Medicine, Continuing Educationxe2x80x94Public Service Extension (2001). The uncertainty with respect to a specific causal factor, makes diagnosis, and in turn, treatment, of podotrochlosis very difficult.
In the anatomy of the horse""s leg, the distal sesamoid bone, commonly known as the navicular bone, is located in the lower portion of the hoof, directly behind the pedal or coffin bone, wedged between the pedal bone and the short pastern bone. The navicular bone is connected to other bones in the hoof by the impar ligaments. The deep digital flexor tendon stretches from the pedal bone, under the navicular bone, upwards to the upper portion of the back of the horse""s leg.
The navicular bone serves two important functions: 1) by being wedged between the pedal bone and short pastern, it increases the size of the pedal joint, allowing the joint to absorb more stress and concussion; and 2) it maintains the angle of the deep digital flexor tendon and acts as a pulley on the tendon, which takes a significant amount of stress off the pedal bone by absorbing a majority of it. McNamee, C., xe2x80x9cNavicular Syndromexe2x80x9d www.equusite.com. (1998).
Podotrochlosis may be initiated following injury to the deep digital flexor tendon, such as bruises, adhesions, torn fibers and fibrillation or fraying. When injured, the movement of the tendon may be greatly limited, which can lead to erosion of the navicular bone. In the alternative, the navicular bone itself can deteriorate, producing jagged or sharp bone edges that can tear or otherwise injure the deep digital flexor tendon as it continually stretches over it. Poor blood supply, caused by thrombosis or blood clots, leads to low oxygen levels in the navicular bone, resulting in pain and causing deterioration of the bone. Podotrochlosis may also be the result of foot imbalance, such as medio-lateral foot imbalance, or an abnormal foot conformation, such as a long toe/low heel conformation, sheared heels or small feet, which can lead to a broken backward hoof-pastern axis.
Podotrochlosis is thus a dynamic problem, and its effects are seen with every step the horse takes. With each stride, the horse lifts up the leg, moves it, and then lowers it to bear weight. The individual anatomical parts of the foot are loaded and unloaded, stretched and relaxed, time after time. Once the condition has been initiated, the resultant pathology will include bone changes, cartilage changes, tendon changes and ligament changes.
Currently, there is no one treatment for podotrochlosis that is effective in all cases. Common non-medical treatments include rest from demanding and repetitive work and improved foot care, including trimming and shoeing. Medical treatments include drug therapy and correction of the hoof by surgery. Riegl, R J and Hakola S E, Illustrated Atlas of Clinical Equine Anatomy and Common Disorders of the Horse, Equista Publications, Ohio, USA (1996).
Pharmaceutical therapy may include treatment to increase vascular circulation to the feet, as well as symptomatic treatment to reduce inflammation and relieve pain. Commonly used drugs include isoxsuprine and warfarin, non-steroidal anti-inflammatory drugs (NSAIDS) and corticosteroids, and polysulfated glycosaminoglycans. Isoxsuprine is known to dilate deep blood vessels and improve circulation; warfarin is a thrombolytic drug, which dissolves blood clots and improves circulation. NSAIDS and corticosteroids reduce pain and inflammation, and some NSAIDS are also believed to reduce blood clotting. Glycosamine compounds are given to help protect cartilage from further deterioration. A more aggressive pharmaceutical therapy involves the injection of ammonium chloride into the palmar digital nerve, thus blocking pain and allowing the horse to use its foot in a normal manner.
While pharmaceutical treatment can and often does provide relief from the condition, a pharmaceutical cure for podotrochlosis has not yet been realized, and once administration of the particular chosen drug has ceased, symptoms will reoccur. In addition, it is commonly known that drug therapy is frequently associated with one or more side effects, some of which may be adverse or even fatal.
Surgical treatments include correction of the shape and position of a damaged hoof, as well as treatment to reduce pain. Correction of the hoof is recommended if a broken backwards hoof pastern axis occurs, leading to a long toe/low heel conformation, or in cases where the heels have collapsed badly. Following corrective surgery, orthopedic horse shoes are typically applied. While this type of surgery clearly has a palliative effect, it does not cure the cause for the lameness, and can not be viewed as a curative treatment.
Other surgical treatments include palmar digital neurectomy, wherein the palmar digital nerves are severed, and desmotomy, wherein the suspensory navicular ligaments are cut to relieve pressure on the navicular bone and enable the deep digital flexor muscle to stretch. With respect to neurectomy, as this procedure prevents the horse from feeling pain in the heel area (although sensation to the toe remains), careful supervision is required to avoid injury and/or infection. In addition, the benefits of this type of surgery typically last for only about a year or so, as the severed nerves will almost always regrow. McNamee, C., xe2x80x9cNavicular Syndromexe2x80x9d www.equusite.com, (1998).
Thus, while there are methods for treating podotrochlosis, there is no cure. Moreover, each of the known treatments is associated with its own set of drawbacks and side effects. The present invention overcomes these disadvantages and provides a method for the treatment of podotrochlosis that yields superior, long-lasting results with minimal side-effects and trauma for the animal patient.
The present invention provides a method for treating podotrochlosis in the foot of a horse that involves the use of a sonar-emitting/shockwave-emitting device to identify specific area(s) within the foot affected by podotrochlosis and to subsequently deliver one or more extracorporeal shockwaves directly to the identified area(s).
In accordance with the principles of the invention, the hoof of an affected animal is first softened, then cut and shaped as needed, and then an anesthetic agent is administered to the animal to relax at least the deep digital flexor muscle (musculus flexor digitalis profundus) and the associated tendon, which are then flexed or extended to a desired extent. Specific areas within the foot affected by the condition are identified, preferably by use of a sonar-emitting device. Preferably, a sonar transmission-enhancing agent is applied to the hoof, prior to application of the sonar-emitting device. Once the affected areas have been identified, a shockwave-emitting device is applied to the hoof, and at least one extracorporeal shockwave is directed at each of the affected areas.
In various embodiments of the method, the hoof is softened by soaking in an aqueous solution, preferably of about 0.9% NaCl. The extent of flexion or extension of the deep digital flexor muscle and tendon will preferably result in a prolongation of between about 20% and 100%, and preferably, between about 35% and 80% of the natural length. The preferred agent for enhancing sonar transmission is paraffin.